1. Field of the Invention
The present invention relates to a resinous connector which is welded to resinous containers having an opening so as to cover the opening, and whose leading end is fitted into a hose by press-in fitting and is fastened thereto. A resinous connector according to the present invention can be used as connectors for cut-off valves which are disposed in resinous fuel tanks, and as connectors for breather tubes.
2. Description of the Related Art
Fuel tanks boarded on automobiles have been more and more made of resin in view the lightweight requirement. Fuel tanks are required to prohibit fuels from permeating. Accordingly, it is necessary to use resinous materials, whose gas-barrier property is good, for making fuel tanks. As a resin whose gas-barrier property is appropriate for the application, polyamide resins have been known. However, polyamide resins have a disadvantage in that they might be insufficient in terms of strengths such as shock resistance. Hence, Japanese Unexamined Patent Publication (KOKAI) No. 2002-160,537, for example, discloses a two-layered fuel tank in which a polyamide resin which is good in terms of the gas-barrier property is laminated with a polyethylene resin which is good in terms of the shock resistance as well as the weldablity to other component parts. In the two-layered fuel tank the polyamide resin makes the inner layer, and the polyethylene resin makes the, outer layer.
Moreover, it is necessary to fasten various resinous component parts, such as cut-off valves, valves for detecting filled-up fuel tanks, filler pipes and breather pipes, to automotive fuel tanks. In this instance, when a fuel tank has an outer layer made of a polyethylene resin and a resinous component part is formed of a polyethylene resin at least at the portions to be fastened to the fuel tank, it is preferable because the resinous component part can be fastened to the fuel tank by welding and the sealing property is improved remarkably between the resinous component part and the fuel tank.
Japanese Unexamined Patent Publication (KOKAI) No. 2002-293,144, for instance, discloses such a resinous component part. It has been known that the resinous component part comprises a body which is composed of a gas-impermeable resin such as polyamide resins, at least a part of which is covered with an adhesive resinous material such as high-density polyethylene resins. The resinous component part is used in the following manner: the cover layer composed of the adhesive resinous material is welded to fuel tanks; and the nipple composed of the gas-impermeable resin is fitted into hoses by press-in fitting. Moreover, Japanese Unexamined Patent Publication (KOKAI) No. 6-270,701 discloses a pipe fitting which comprises a portion to be welded to fuel tanks, the portion being composed of a high-density polyethylene resin, and a fitting bonded to the leading end of the portion and composed of a polyamide resin. The thus constructed resinous component parts can be fastened by welding to fuel tanks, and can securely inhibit fuels from permeating through the fastened parts. In addition, since the polyamide resin exhibits good creep resistance, the resinous component parts can maintain high reliability for a long period of time in service such as when the fitting or nipple is fitted into hoses.
However, when the regulation pertaining the fuel permeation is strict, resinous component parts whose nipple is formed of polyamide resins might be insufficient in terms of the sealing property when the connector is simply fitted into hoses by press-in fitting. Accordingly, it has been a usual practice conventionally to hold an O-ring at the leading end of the nipple and have the O-ring pressed onto the hoses and nipple, thereby securing the sealing property.
However, when resinous component parts are constructed so that an O-ring is held to the leading end of the nipple, the O-ring is rubbed in the period of from the initial press-in fitting to the final press-in fitting into hoses. Accordingly, O-rings might be twisted or bruised. Consequently, various countermeasures have been devised, for example, reducing the thickness of O-rings, or forming the cross-section of O-rings anomalously, If such is the case, however, no further improvement of the sealing property can be expected because the tightening allowance of O-rings has become smaller. Thus, the problem of increased cost has arisen because no standard O-rings can be applied to resinous component parts.
Moreover, the connector composed of polyamide resins exhibits low shock resistance. Accordingly, in resinous component parts whose nipple projects perpendicularly to the surface of fuel tanks, a problem occurs in that there are many limitations in designing the resinous component parts, because stresses concentrate at the root of the nipple so much that the nipple might break at the root. Consequently, it is possible to think of covering the surface of the nipple with polyethylene resins which exhibit high toughness. In this instance, however, a problem arises in that the load for pulling out hoses has lowered gradually because the cover layer composed of polyethylene resins is fatigued by stresses.